Obviously the Legacy door and window frames would dictate the size and format of the finished building and would need to be designed around regarding their size and format.
I used Visio as a scale design tool. I input all the existing UPVC frame sizes and then played about with possible variations. I wanted to abut the building onto an existing party wall and not protrude too far into the garden. As there was an existing path (although not very good!) I took this as the extremity of the building width. I roughly judged the length to fit in with an existing garden shed and another old path 90degrees to the first one. Unfortunately I couldn’t make the height as low I would have liked as the door frames are full size suited to a main dwelling. This meant the base would need to be of minimal depth and the roof pitch also kept to the minimal. I had hoped for a greenhouse style pitched roof but this would result in the final building being way too tall. I made some wooden scale models once I had decided the final format to show my neighbours so that they could have some input if they wanted to.
Some other Structural considerations were that I didn’t want the building to overhang my neighbours wall or to lean against it or hang on it. Garden walls aren’t particularly strong structurally and ours was over 100 years old. I also wanted to be able to gather rainwater from it to use in my veg garden. After weeks of planning and deliberation I came up with the offset ridge design. Not as easy to build as first envisaged but it ticked all the boxes.